/ Wide angle converter

Being too skint to afford a wide angle lens for my D80, are the wide angle converters that you can screw onto the filter mount any good at all? I'm only looking at occasional use.

I guess I can expect some vignetting, but are there any other downfalls? I can get one for £48, which is a lot cheaper than the Nikon 10-20mm. I know you get what you pay for, but would I be wasting £48?

You can have it if you like, no use to me anymore as I had a mandatory upgrade recently rendering it obsolete. I have had some good results with it and you can cut out a lot of the chromatic aberation in camera raw in photoshop, but that's not to say you might not still get comments like this:http://www.ukhillwalking.com/images/dbpage.html?id=150429

email me an address and I'll send it to you. Might take a while what with it being Christmas and all.